High performance processor chips, which are also known as microchips or integrated circuits (ICs), are often tested and subsequently sorted based on their performance and matched to a given class of machine. Individual chips are tested prior to installation on modules in machines in order to identify chip failures, allowing higher machine manufacturing productivity and improving product quality. Test equipment developed to support performance, productivity and quality is usually required to meet functional test limits defined by several boundary variables such as chip/module voltage, clock speed, power dissipation, and temperature.
Chip testers such as functional or non-functional testers may detect chip failures during testing at different operating temperatures. Chips are typically tested at operating temperatures they might encounter in the field so that failures are eliminated before the chip reaches the customer. Additionally, testing chips at particular operating temperatures may facilitate determining particular failure modes. For example, chip testing often requires the chips to be cooled to low temperatures in order to find certain possible failures, including temperatures as low as −20 degrees Celsius (C.). Some early use failures which might not have normally occurred until after reaching a customer may be found during testing at elevated temperatures. As an example, a faulty interconnection on a chip can be detected by testing at either low or high temperatures. In this example, two conductors may touch each other with sufficient force that an electrical connection is made even though the parts are not mechanically interconnected. Such a part may pass tests and reach a customer, but will likely fail at a higher frequency rate than is acceptable. If a chip is tested at these temperatures, this marginal interconnection may separate and thereby identify the faulty part.
The performance of a chip also often varies based on the operating temperature of the chip, making temperature control of the chip an integral part of chip testing. Accurate temperature control over a wide range of temperatures during chip testing processes allows verification of whether a processor functions at all, as well as it how it performs. For example, accurate temperature control allows a chip tester to determine whether a processor of a chip functions at a particular temperature and more specifically how many of its processor cores function at that temperature. Testing with precise control over the chip temperature and local temperature distribution also allows more precise determination of chip speed, helping to minimize the guardband (i.e., extra margin) that is put into the acceptance criteria for a good chip, allowing an increase in the manufacturing yield. Another benefit of accurately controlling the temperature of a chip during testing is more precise determination of power dissipation of the chip during product level conditions. Precise determination of power dissipation facilitates directing higher power chips to products that have greater power supply and cooling capacity while directing lower power chips to products with less capacity. This may increase chip yield as all chips are not required to function to the more restrictive conditions of less capable systems.
Failure to precisely control thermal conditions during chip testing may result in finding fewer faults, having to increase the guardband on sorted speed, and reduced ability to determine power dissipation. These failures may result in lower chip yields, lower customer satisfaction, higher warranty costs, and overall decrease in efficiency in chip production. These problems are exacerbated as chips become more and more powerful, as more powerful chips often require more precise temperature control due to their higher frequency, higher leakage, and higher power dissipation. There is, therefore, a need for an effective and efficient system to control temperatures in a chip tester system. There is an even greater need for such a system as chips become more and more powerful and require more accurate temperature control.